The present invention relates to a process for producing practically anhydrous acetone by means of extractive distillation, the acetone being contained in reaction mixtures derived for example, from the synthesis of acetone from isopropyl alcohol and the synthesis of methylisobutyl ketone from acetone. More particularly, this invention relates to a process using isopropyl alcohol as the extracting agent in the purification of acetone by distillation, wherein the isopropyl alcohol is recycled and may be present in the afore-mentioned reaction mixtures.
Numerous proposals have been made to remove water from acetone which may have been prepared by different methods. These proposals usually are related to the particular production process, that is, the raw product mixture which is produced is treated to yield the desired products and these products are further treated for maximum purity. Thus, the preparation of acetone from isopropyl alcohol, ethanol, acetylene, acetaldehyde or acetic acid by dehydrogenation, oxidation, or catalytic hydrogenation in the vapor phase generally yields acetone vapor in admixture with different vapors. German Auslegeschrift No. 1,012,909 proposes a simplified distillation process for removing acetone from the afore-mentioned vapor mixtures and dehydrating it by passing the mixture of hot gases and vapors derived from the acetone synthesis through a column in counter-current flow direction relative to a liquid flowing downward, using the sensible and latent heat of the gases and vapors for concentrating the acetone and removing it from the remaining acetone-containing liquids. The water content of the acetone so obtained ranges from 0.02 to 0.10 weight percent.
German Auslegeschrift No. 1,266,746 proposes to remove acetone from a mixture containing acetone, methyl acetate and methanol by subjecting the mixture to a predistillation to remove higher-boiling components therefrom, taking into consideration that the hydrocarbons which are present interfere with the extractive distillation by means of water; the overhead product obtained from the predistillation is subjected to a liquid-liquid extraction using water, and the layer of lighter hydrocarbons is removed; finally, the aqueous extract is subjected to extractive distillation with water, the bottoms product obtained is subjected to fractional distillation, and acetone, containing 0.43 weight percent water, is obtained as the overhead product.
Other methods for removing water from acetone or for concentrating aqueous acetone fluids have been disclosed in German Auslegeschrift No. 1,793,516 and German Offenlegungschrift No. 2,047,614. The process disclosed in said German Auslegeschrift employs molecular sieves using zeolites, having pore diameters ranging from 4 to 5A, to free the acetone from methanol, water, and other contaminants. In order to reduce formation of by-products when the acetone comes in contact with the zeolite, it is necessary to employ specific contacting times and contacting temperatures. According to the above mentioned German Offenlegungsschrift, the pervaporation technique (evaporation through a membrane) is employed in order to obtain a "pure" acetone containing 0.5 wt.% water.
The object of the present invention is to dehydrate an acetone of the type occurring, for example, in reaction mixtures derived from the catalytic dehydrogenation of isopropyl alcohol and from the methylisobutyl ketone synthesis of acetone including condensation, dehydration, and hydrogenation, to a water content of less than 0.2 weight percent.
Another object of this invention is to remove the water by the use of a reaction component of the reaction mixtures occurring in the conventional acetone production process.
Finally, it is an object of this invention to remove the water from acetone by an economical manner in existing plants taking environmental factors into account.